Designer s Guide to the Cypress PSoC

Transcription

1 Designer s Guide to the Cypress PSoC By Robert Ashby July 2005 ISBN Paperback 272 Pages $51.95 Features: The first independent technical reference available on the PSoC, a product line experiencing explosive growth in the embedded design world Application examples, sample code, and design tips and techniques will get readers get up-to-speed quickly Companion CD-ROM includes all example code from book, so that engineers can easily adapt it to their own designs This it the first technical reference book available on the PSoC, and it offers the most comprehensive combination of technical data, example code, and descriptive prose you ll find anywhere. Embedded design expert Robert Ashby will guide you through the entire PSoC world, providing thorough coverage of device feature, design, programming and development of the softwarereconfigurable PSoC. He shares his best tips, tricks, and techniques that will help you to utilize the flexible and inexpensive PSoC to its greatest potential, with a minimum of heartaches and late nights. With its emphasis on designing for adaptability - a feature of the utmost importance in today s fast-paced and cost-pressured design cycles - this book will bring you up to speed quickly on everything PSoC, from memory management to interconnects. You will add brains and capable signal conditioning to a design with one chip, giving you extreme flexibility for a relatively low price. Specific application examples highlighting the PSoC s unique capabilities are included throughout the text, with the supporting sample source code. This valuable code is also provided on the companion CD-ROM so you can easily adapt it to your own designs. Order from Newnes. Mail: Elsevier Science, Order Fulfillment, Westline Industrial Dr., St. Louis, MO Phone: US/Canada , (Intl.) Fax: , (Intl.) usbkinfo@elsevier.com Visit Newnes on the Web:

2 Table of Contents Introduction to Microcontroller Basics Chapter 1: Why Use the Cypress PSoC? Chapter 2: Structure of the PSoC Chapter 3: PSoC Designer Chapter 4: Improvements of the PSoC Chapter 5: Limitations of the PSoC Chapter 6: PSoC Modules Chapter 7: Interconnects Chapter 8: PSoC Memory Management Chapter 9: Multiple Configurations Chapter 10: Project Pruning Chapter 11: Design Tips Chapter 12: PSoC Express Appendix A: Global Resources Appendix B: Project Walkthrough Appendix C: Limited Analog System

3 Chapter 2 The price and availability of materials Chapter contents 2.1 Introduction Data for material prices The use-pattern of materials Ubiquitous materials Exponential growth and consumption doubling-time Resource availability The future Conclusion 27 Examples 27

4 18 Chapter 2 The price and availability of materials 2.1 Introduction In the first chapter we introduced the range of properties required of engineering materials by the design engineer, and the range of materials available to provide these properties. We ended by showing that the price and availability of materials were important and often overriding factors in selecting the materials for a particular job. In this chapter we examine these economic properties of materials in more detail. 2.2 Data for material prices Table 2.1 ranks materials by their relative cost per unit weight. The most expensive materials diamond, platinum, gold are at the top. The cheapest cast iron, wood, cement are at the bottom. Such data are obviously important in choosing a material. How do we keep informed about materials price changes and what controls them?. The Financial Times and the Wall Street Journal give some, on a daily basis. Trade supply journals give more extensive lists of current prices. A typical such journal is Procurement Weekly, listing current prices of basic materials, together with prices 6 months and a year ago. All manufacturing industries take this or something equivalent the workshop in your engineering department will have it and it gives a guide to prices and their trends. Figure 2.1 shows the variation in price of two materials copper and rubber. These short-term price fluctuations have little to do with the real scarcity or abundance of materials. They are caused by small differences between the rate of supply and demand, much magnified by speculation in commodity futures. The volatile nature of the commodity market can result in large changes over a period of a few days that is one reason speculators are attracted to it and there is little that an engineer can do to foresee these changes. Political factors are also extremely important a scarcity of cobalt in 1978 was due to the guerilla attacks on mineworkers in Zaire, the world s principal producer of cobalt; the low price of aluminum and diamonds in 1995 was partly caused by a flood of both from Russia at the end of the Cold War. The long-term changes are of a different kind. They reflect, in part, the real cost (in capital investment, labor, and energy) of extracting and transporting the ore or feedstock and processing it to give the engineering material. Inflation and increased energy costs obviously drive the price up; so, too, does the necessity to extract materials, like copper, from increasingly lean ores; the leaner the ore, the more machinery and energy are required to crush the rock containing it, and to concentrate it to the level that the metal can be extracted. In the long term, then, it is important to know which materials are basically plentiful, and which are likely to become scarce. It is also important to know the extent of our dependence on materials.

5 2.2 Data for material prices 19 Table 2.1 Approximate relative price per tonne (mild steel ¼ 100) Material Relative price $ Diamonds, industrial 200m Platinum 5m Gold 2m Silver 150,000 CFRP (mats. 70% of cost; fabr. 30% of cost) 20,000 Cobalt/tungsten carbide cermets 15,000 Tungsten 5000 Cobalt alloys 7000 Titanium alloys 10,000 Nickel alloys 20,000 Polyimides 8000 Silicon carbide (fine ceramic) 7000 Magnesium alloys 1000 Nylon Polycarbonate 1000 PMMA 700 Magnesia, MgO (fine ceramic) 3000 Alumina, Al 2 O 3 (fine ceramic) 3000 Tool steel 500 GFRP (mats. 60% of cost; fabr. 40% of cost) 1000 Stainless steels 600 Copper, worked (sheets, tubes, bars) 400 Copper, ingots 400 Aluminum alloys, worked (sheet, bars) 400 Aluminum ingots 300 Brass, worked (sheet, tubes, bars) 400 Brass, ingots 400 Epoxy 1000 Polyester 500 Glass 400 Foamed polymers 1000 Zinc, worked (sheet, tubes, bars) 400 Zinc, ingots 350 Lead, worked (bars, sheet, tube) 250 Lead, ingots 200 Natural rubber 300 Polypropylene 200 Polyethylene, high density 200 Polystyrene 250 Hard woods 250 Polyethylene, low density 200 Polyvinyl chloride 300 Plywood 200 Low-alloy steels 130

6 20 Chapter 2 The price and availability of materials Table 2.1 (Continued) Material Relative price $ Mild steel, worked (angles, sheet, bars) 100 Cast iron 90 Iron, ingots 70 Soft woods 70 Concrete, reinforced (beams, columns, slabs) 50 Fuel oil 50 Cement 20 Coal 20 Copper Rubber tonne tonne S O N D J F M A M S O N D J F M A M Figure 2.1 Recent fluctuations in the price of copper and rubber. 2.3 The use-pattern of materials The way in which materials are used in an industrialized nation is fairly standard. It consumes steel, concrete, and wood in construction; steel and aluminum in general engineering; copper in electrical conductors; polymers in appliances, and so forth; and roughly in the same proportions. Among metals, steel is used in the greatest quantities by far: 90 percent of all the metal produced in the world is steel. But the nonmetals wood and concrete beat steel they are used in even greater volume. About 20 percent of the total import bill is spent on engineering materials. Table 2.2 shows how this spend is distributed. Iron and steel, and the raw materials used to make them, account for about a quarter of it. Next are wood and lumber widely used in light construction. More than a quarter is spent on the metals copper, silver, aluminum, and nickel. All polymers taken together, including rubber, account for little more than 10 percent. If we include the further metals zinc, lead, tin, tungsten, and mercury, the list accounts for

7 2.4 Ubiquitous materials 21 Table 2.2 Imports of engineering materials, raw, and semis: percentage of total cost Iron and steel 27 Wood and lumber 21 Copper 13 Plastics 9.7 Silver and platinum 6.5 Aluminum 5.4 Rubber 5.1 Nickel 2.7 Zinc 2.4 Lead 2.2 Tin 1.6 Pulp/paper 1.1 Glass 0.8 Tungsten 0.3 Mercury 0.2 Etc percent of all the money spent abroad on materials, and we can safely ignore the contribution of materials which do not appear on it. 2.4 Ubiquitous materials The composition of the earth s crust Let us now shift attention from what we use to what is widely available. A few engineering materials are synthesized from compounds found in the earth s oceans and atmosphere: magnesium is an example. Most, however, are won by mining their ore from the earth s crust, and concentrating it sufficiently to allow the material to be extracted or synthesized from it. How plentiful and widespread are these materials on which we depend so heavily? How much copper, silver, tungsten, tin, and mercury in useful concentrations does the crust contain? All five are rare: workable deposits of them are relatively small, and are so highly localized that many governments classify them as of strategic importance, and stockpile them. Not all materials are so thinly spread. Table 2.3 shows the relative abundance of the commoner elements in the earth s crust. The crust is 47 percent oxygen by weight or because oxygen is a big atom, it occupies 96 percent of the volume (geologists are fond of saying that the earth s crust is solid oxygen

8 22 Chapter 2 The price and availability of materials Table 2.3 Abundance of elements Crust Oceans Atmosphere Element weight % Element weight % Element weight % Oxygen 47 Oxygen 85 Nitrogen 79 Silicon 27 Hydrogen 10 Oxygen 19 Aluminum 8 Chlorine 2 Argon 2 Iron 5 Sodium 1 Carbon dioxide 0.04 Calcium 4 Magnesium 0.1 Sodium 3 Sulphur 0.1 Potassium 3 Calcium 0.04 Magnesium 2 Potassium 0.04 Titanium 0.4 Bromine Hydrogen 0.1 Carbon Phosphorus 0.1 Manganese 0.1 Fluorine 0.06 Barium 0.04 Strontium 0.04 Sulphur 0.03 Carbon 0.02 * The total mass of the crust to a depth of 1 km is kg; the mass of the oceans is kg; that of the atmosphere is kg. containing a few percent of impurities). Next in abundance are the elements silicon and aluminum; by far the most plentiful solid materials available to us are silicates and alumino-silicates. A few metals appear on the list, among them iron and aluminum both of which feature also in the list of widely used materials. The list extends as far as carbon because it is the backbone of virtually all polymers, including wood. Overall, then, oxygen and its compounds are overwhelmingly plentiful on every hand we are surrounded by oxideceramics, or the raw materials to make them. Some materials are widespread, notably iron and aluminum; but even for these the local concentration is frequently small, usually too small to make it economic to extract them. In fact, the raw materials for making polymers are more readily available at present than those for most metals. There are huge deposits of carbon in the earth: on a world scale, we extract a greater tonnage of carbon every month than we extract iron in a year, but at present we simply burn it. And the second ingredient of most polymers hydrogen is also one of the most plentiful of elements. Some materials iron, aluminum, silicon, the elements to make glass, and cement are plentiful and widely available. But others mercury, silver, tungsten are examples are scarce and highly localized, and if the current pattern of use continues may not last very long.

9 2.5 Exponential growth and consumption doubling-time Exponential growth and consumption doubling-time How do we calculate the lifetime of a resource like mercury? Like almost all materials, mercury is being consumed at a rate which is growing exponentially with time (Figure 2.2), simply because both population and living standards grow exponentially. We analyze this in the following way. If the current rate of consumption in tonnes per year is C then exponential growth means that dc dt ¼ r 100 C ð2:1þ where, for the generally small growth rates we deal with here (1 5 percent per year), r can be thought of as the percentage fractional rate of growth per year. Integrating gives C ¼ C 0 exp rðt t 0Þ ð2:2þ 100 where C 0 is the consumption rate at time t ¼ t 0. The doubling-time t D of consumption is given by setting C/C 0 ¼ 2 to give t D ¼ 100 r log e 2 70 ð2:3þ r Steel consumption is growing at less than 2 percent per year it doubles about every 35 years. Polymer consumption is rising at about 5 percent per dc dt r = C 100 C (tonne year 1 ) C 0 t 0 Area = consumption between t 0 and t Time t (year) Figure 2.2 The exponentially rising consumption of materials.

10 24 Chapter 2 The price and availability of materials year it doubles every 14 years. During times of boom the 1960s and 1970s for instance polymer production increased much faster than this, peaking at 18 percent per year (it doubled every 4 years), but it has now fallen back to a more modest rate. 2.6 Resource availability The availability of a resource depends on the degree to which it is localized in one or a few countries (making it susceptible to production controls or cartel action); on the size of the reserves, or, more accurately, the resource base (explained shortly); and on the energy required to mine and process it. The influence of the last two (size of reserves and energy content) can, within limits, be studied and their influence anticipated. The calculation of resource life involves the important distinction between reserves and resources. The current reserve is the known deposits which can be extracted profitably at today s price using today s technology; it bears little relationship to the true magnitude of the resource base; in fact, the two are not even roughly proportional. The resource base includes the current reserve. But it also includes all deposits that might become available given diligent prospecting and which, by various extrapolation techniques, can be estimated. And it includes, too, all known and unknown deposits that cannot be mined profitably now, but Identified ore Undiscovered ore Minimum mineable grade Economic Reserve Increased prospecting Not economic Improved mining technology Resource base (includes reserve) Decreasing degree of economic feasibility Decreasing degree of geological certainty Figure 2.3 The distinction between the reserve and the resource base, illustrated by the McElvey diagram.

11 2.6 Resource availability 25 which due to higher prices, better technology or improved transportation might reasonably become available in the future (Figure 2.3). The reserve is like money in the bank you know you have got it. The resource base is more like your total potential earnings over your lifetime it is much larger than the reserve, but it is less certain, and you may have to work very hard to get it. The resource base is the realistic measure of the total available material. Resources are almost always much larger than reserves, but because the geophysical data and economic projections are poor, their evaluation is subject to vast uncertainty. Although the resource base is uncertain, it obviously is important to have some estimate of how long it can last. Rough estimates do exist for the size of the resource base, and, using these, our exponential formula gives an estimate of how long it would take us to use up half of the resources. The half-life is an important measure: at this stage prices would begin to rise so steeply that supply would become a severe problem. For a number of important materials these half-lives lie within your lifetime: for silver, tin, tungsten, zinc, lead, mercury, and oil (the feed stock of polymers) they lie between 40 and 70 years. Others (most notably iron, aluminum, and the raw materials from which most ceramics and glasses are made) have enormous resource bases, adequate for hundreds of years, even allowing for continued exponential growth. The cost of energy enters here. The extraction of materials requires energy (Table 2.4). As a material becomes scarcer copper is a good example it must be extracted from leaner and leaner ores. This expends more and more energy, per tonne of copper metal produced, in the operations of mining, crushing, and concentrating the ore; and these energy costs rapidly become prohibitive. The rising energy content of copper shown in Table 2.4 reflects the fact that the richer copper ores are, right now, being worked out. Table 2.4 Approximate energy content of materials (GJ tonne 1 ) Aluminum 280 Plastics Copper 140, rising to 300 Zinc 68 Steel 55 Glass 20 Cement 7 Brick 4 Timber Gravel 0.2 Oil 44 Coal 29

12 26 Chapter 2 The price and availability of materials 2.7 The future How are we going to cope with the shortages of engineering materials in the future? One way obviously is by Material-efficient design Many current designs use far more material than is necessary, or use potentially scarce materials where the more plentiful would serve. Often, for example, it is a surface property (e.g. low friction, or high corrosion resistance) which is wanted; then a thin surface film of the rare material bonded to a cheap plentiful substrate can replace the bulk use of a scarcer material. Another way of coping with shortages is by Substitution It is the property, not the material itself, that the designer wants. Sometimes a more readily available material can replace the scarce one, although this usually involves considerable outlay (new processing methods, new joining methods, etc.). Examples of substitution are the replacement of stone and wood by steel and concrete in construction; the replacement of copper by polymers in plumbing; the change from wood and metals to polymers in household goods; and from copper to aluminum in electrical wiring. There are, however, technical limitations to substitution. Some materials are used in ways not easily filled by others. Platinum as a catalyst, liquid helium as a refrigerant, and silver on electrical contact areas cannot be replaced; they perform a unique function they are, so to speak, the vitamins of engineering materials. Others a replacement for tungsten for lamp filaments, for example would require the development of a whole new technology, and this can take many years. Finally, substitution increases the demand for the replacement material, which may also be in limited supply. The massive trend to substitute plastics for other materials puts a heavier burden on petrochemicals, at present derived from oil. A third approach is that of Recycling Recycling is not new: old building materials have been recycled for millennia; scrap metal has been recycled for centuries; both are major industries. Recycling is labor intensive, and therein lies the problem in expanding its scope. Over the last 30 years, the rising cost of labor made most recycling less than economic.

13 Examples Conclusion Overall, the materials-resource problem is not as critical as that of energy. Some materials have an enormous base or (like wood) are renewable and fortunately these include the major structural materials. For others, the resource base is small, but they are often used in small quantities so that the price could rise a lot without having a drastic effect on the price of the product in which they are incorporated; and for some, substitutes are available. But such adjustments can take time up to 25 years if a new technology is needed; and they need capital too. Rising energy costs mean that the relative costs of materials will change in the next 20 years: designers must be aware of these changes, and continually on the look-out for opportunities to use materials as efficiently as possible. But increasingly, governments are imposing compulsory targets on recycling materials from a wide range of mass-produced consumer goods (such as cars, electronic equipment, and white goods). Manufacturers must now design for the whole life cycle of the product: it is no longer sufficient for one s mobile phone to work well for two years and then be thrown into the trash can it must also be designed so that it can be dismantled easily and the materials recycled into the next generation of mobile phones. Environmental impact As well as simply consuming materials, the mass production of consumer goods places two burdens on the environment. The first is the volume of waste generated. Materials which are not recycled go eventually to landfill sites, which cause groundwater pollution and are physically unsustainable. Unless the percentage of materials recycled increases dramatically in the near future, a significant proportion of the countryside will end up as a rubbish dump. The second is the production of the energy necessary to extract and process materials, and manufacture and distribute the goods made from them. Fossil fuels, as we have seen, are a finite resource. And burning fossil fuels releases carbon dioxide into the atmosphere, with serious implications for global warming. Governments are already setting targets for carbon dioxide emissions and also imposing carbon taxes the overall effect being to drive up energy costs. Examples 2.1 (a) Commodity A is currently consumed at the rate C A tonnes per year, and commodity B at the rate C B tonnes per year (C A > C B ). If the two consumption rates are increasing exponentially to give growths in consumption after each year of r A % and r B %, respectively (r A < r B ), derive

14 28 Chapter 2 The price and availability of materials an equation for the time, measured from the present day, before the annual consumption of B exceeds that of A. (b) The table shows figures for consumption and growth rates of steel, aluminum and plastics. What are the doubling-times (in years) for consumption of these commodities? (c) Calculate the number of years before the consumption of (a) aluminum and (b) polymers would exceed that of steel, if exponential growth continued. Material Current consumption (tonnes year 1 ) Projected growth rate in consumption (% year 1 ) Iron and steel Aluminum Polymers Answers ðaþ t ¼ 100 ln C A r B r A C B (b) Doubling-times: steel, 35 years; aluminum, 23 years; plastics, 18 years. (c) If exponential growth continued, aluminum would overtake steel in 201 years; polymers would overtake steel in 55 years. 2.2 Discuss ways of conserving engineering materials, and the technical and social problems involved in implementing them. 2.3 (a) Explain what is meant by exponential growth in the consumption of a material. (b) A material is consumed at C 0 tonne year 1 in Consumption in 2005 is increasing at r% year 1. If the resource base of the material is Q tonnes, and consumption continues to increase at r% year -1, show that the resource will be half exhausted after a time, t1, given by 2 t 1=2 ¼ 100 r In rq þ 1 200C Discuss, giving specific examples, the factors that might cause a decrease in the rate of consumption of a potentially scarce material.